Producing cut surfaces in a transparent material by means of optical radiation

ABSTRACT

A method for producing a cut surface in a transparent material using optical radiation. A laser device separates the material using optical radiation and includes an optical unit focussing the radiation along an optical axis into an image field defining an image-field size. A focal position is adjusted transversely along the axis, producing a cut surface extending substantially parallel to the axis and, in projection along the axis, is a curve having a maximum extent. The focus is displaced by adjustment of the focal position along a trajectory curve lying in the cut surface. The cut surface has a maximum extent which is greater than the image-field size. The focal position is moved transverse to the axis along the curve. The image field is displaced transversely, and the focal position is adjusted in an oscillating fashion along the axis on the curve between an upper and lower axial focus position.

PRIORITY CLAIM

The present application is a Continuation Application of U.S. patentapplication Ser. No. 14/353,265, filed Apr. 21, 2014 which is a NationalPhase entry of PCT Application No. PCT/EP2012/070896, filed Oct. 22,2012, which claims priority from German Application Number102011085046.5, filed Oct. 21, 2011, the disclosures of which are herebyincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method for producing a cut in a transparentmaterial by means of optical radiation, wherein a laser device is usedwhich is adapted to generate a cut within the transparent material bymeans of the optical radiation and which comprises optics which focusthe optical radiation along an optical axis into a focus situated in thematerial and which have in the material an image field in which thefocus lies and which has an image field size, wherein a position of thefocus is moved transverse to the optical axis and along the opticalaxis, wherein the cut extends parallel to the optical axis and is acurve in projection along the optical axis and has a maximum extent inprojection along the optical axis, and wherein the focus is shifted bythe movement of the position of the focus along a path lying in the cut.

The invention further relates to a method for producing control data forproducing a cut in a transparent material, wherein the control data areadapted for a laser device which is adapted to generate the cut withinthe transparent material by means of optical radiation and whichcomprises optics which focus the optical radiation along an optical axisinto a focus situated in the material and which have in the material animage field in which the focus lies and which has an image field size,wherein the laser device further comprises a focus adjustment device formoving a position of the focus transverse to the optical axis and alongthe optical axis, wherein the control data predetermine a path alongwhich the position of the focus of the optical radiation is to be movedin the material to produce the cut in such a way that the cut extendsparallel to the optical axis, is a curve in a projection along theoptical axis and has a maximum extent in a projection along the opticalaxis.

The invention further relates to a treatment apparatus for producing acut in a transparent material, which comprises a laser device which isadapted to generate a cut within the transparent material by means ofoptical radiation and which has optics which focus the optical radiationalong an optical axis into a focus situated in the material and whichhave in the material an image field in which the focus lies and whichhas an image field size, wherein the apparatus further comprises a focusadjustment device for moving a position of the focus transverse to theoptical axis and along the optical axis, a control device which isconnected to the laser device and controls the laser device such thatthe focus adjustment device moves the position of the focus of theoptical radiation in the material along a path, wherein the controldevice controls the laser device such that the cut extends parallel tothe optical axis, is a curve in projection along the optical axis andhas a maximum extent in projection along the optical axis.

This method and device are used in particular in the field ofophthalmology.

BACKGROUND OF THE INVENTION

In the field of ophthalmology, as well as in other applications, opticalradiation acts inside the material, for example, the tissue, which istransparent to the optical radiation. Non-linear processes are usuallyused which require a focussing of machining radiation, usually pulsedlaser radiation, into the material, i.e., underneath the surface of thematerial. The production of a cut occurs by displacing the position ofthe focus in the material. With the knowledge that forms the basis ofthis description, the shift of the focus does not necessarily requirethat radiation is also emitted into the focus at this time. Inparticular when pulsed laser radiation is used, the focus iscontinuously shifted and laser radiation pulses are only emitted atcertain times during the focus shift. Nevertheless the correspondingoptics and the focus adjustment device operate continuously, which iswhy the term “focus shift” herein is also understood to mean thecorresponding shift of the point at which optical radiation would befocussed, even if such radiation is momentarily not emitted, e.g.,between two laser pulses.

The high focussing of the laser radiation, i.e., a geometricallystrongly delimited focus, is of great importance for non-linear effects,as only then can the necessary power densities in the material beachieved. This applies both to non-linear processes in which anindividual focus already results in an interaction and to processes inwhich several laser radiation pulses which are emitted one after theother interact to achieve a material-cutting effect. In this regard,approaches are also known in which laser radiation pulses are emitted atseveral overlapping focus spots and only the interaction of the severallaser radiation pulses leads to material cutting in the overlap area.

Three-dimensional cuts, which extend parallel to the optical axis of theradiation incidence (of the so-called main direction of incidence), aree.g., required as cylindrical-jacket-shaped cuts in the field ofophthalmology, in particular in cataract surgery. Here a circularopening with a particular diameter is produced in the front of thecapsular bag. The shape of the cut is then a circular cylinder, which isoriented approximately parallel to the optical axis and thus alsoparallel to the main direction of incidence of the optical radiation.

EP 1486185 relates to an apparatus for cataract surgery in which thelaser radiation is conveyed to the handle with the aid of an opticalfiber. A collimator is mechanically adjusted in the handle in order toadjust the position of the focus along the optical axis. The focus cantherefore be adjusted along the optical axis only very slowly as rapidmovement of the collimator would result in undesired vibrations andthermal loading of the handle. Moreover, the use of an optical fiber atthe powers required for eye surgery is extremely problematic.

A method is described in U.S. Pat. No. 7,486,409 and U.S. Pat. No.6,590,670 for rapidly varying the depth position of a focus on the basisof a vibrating tuning fork. At least one lens of an optical arrangementis fixed to the vibrating arm of a tuning fork which is made to vibrateby an electromagnet. For adjusting the depth, DE 10034251 proposesattaching a corner reflector to the vibrating arm of a tuning fork. Thecorner reflector is illuminated with a non-collimated light beam and thepropagation of the light beam which is reflected back is varied byadjusting the position of the corner reflector. If the light beam isfocussed using an objective lens, a rapid variation of the focusposition in the depth direction, i.e., along the optical axis, isobtained. These tuning fork arrangements were proposed for opticalmeasurement technology.

For producing three-dimensional cuts which extend parallel to theoptical axis of the radiation incidence, laser treatment apparatuses areknown which have an optical unit and device for three-dimensional focusadjustment. Such treatment apparatuses shift the focus in the imagefield and supplement this two-dimensional shift with a shift of theimage field plane to obtain a three-dimensional focus position setting.Since the shift of the image field plane is much slower than thetwo-dimensional shift of the focus position in the image plane, caremust be taken with such apparatuses that the image plane shift is neededas little as possible, in order to design the production of cuts to beas rapid as possible. Therefore, for example, spiral-shaped trajectoriesare known from the state of the art, which combine rapid shift in theimage plane with a comparatively slow shift or adjustment of the imageplane position. In this way, for example, cylindrical cuts, which lieparallel to the optical axis, can be produced very quickly.

A disadvantage of this approach is that the optics must be designed suchthat a rapid two-dimensional shift of the focus position is possible inthe image field. The image field size must also be designed such thatdesired cut sizes are covered.

SUMMARY OF THE INVENTION

An object of the invention is therefore to develop methods and machiningdevices such that cuts in particular cylindrical-jacket-shaped cutswhich run substantially parallel to the optical axis and can be producedwith little outlay.

The object is achieved according to an embodiment of the invention by amethod for producing a cut in a transparent material by means of opticalradiation, wherein a laser device is used which is adapted to generate acut within the transparent material by means of the optical radiationand which comprises optics which focus the optical radiation along anoptical axis into a focus situated in the material and which have in thematerial an image field in which the focus lies and which has an imagefield size, wherein a position of the focus is moved transverse to theoptical axis and along the optical axis, as a result of which the cut isproduced, which extends parallel to the optical axis and is, inprojection along the optical axis, a curve which has a maximum extent,and wherein the focus is shifted by moving the position of the focusalong a path, which lies in the cut, wherein, transverse to the opticalaxis, the cut has a maximum extent which is greater than the image fieldsize. In order to shift the focus along the path, the position of thefocus is moved transverse to the optical axis along the curve, whereinthe image field is shifted transverse to the optical axis and theposition of the focus along the optical axis is moved several times inan oscillating manner between an upper axial focus position and a loweraxial focus position during the movement along the curve.

The object is likewise achieved by a method for producing control datafor producing a cut in a transparent material, wherein the control dataare adapted for a laser device which is adapted to generate a cut withinthe transparent material by means of optical radiation and whichcomprises optics which focus the optical radiation along an optical axisinto a focus situated in the material and which have in the material animage field in which the focus lies and which has an image field size,wherein the laser device further comprises a focus adjustment device formoving a position of the focus transverse to the optical axis and alongthe optical axis. The control data predetermine a path along which theposition of the focus of the optical radiation is to be moved in thematerial to produce the cut in such a way that the cut extends parallelto the optical axis and is, in projection along the optical axis, acurve which has a maximum extent, wherein the control data predeterminethe path such that, transverse to the optical axis, the cut has amaximum extent which is greater than the image field size, the controldata define for the focus adjustment device a movement of the positionof the focus along the curve, wherein a shift of the image fieldtransverse to the optical axis is defined and wherein the control datadefine for the focus adjustment device a multi-oscillating movement ofthe position of the focus along the optical axis between an upper axialfocus position and a lower axial focus position during the movementalong the path.

The object is also achieved by a treatment apparatus for producing a cutin a transparent material, the apparatus comprising a laser device thatis adapted to generate a cut within the transparent material by means ofoptical radiation and that has optics which focus the optical radiationalong an optical axis into a focus situated in the material and whichhas in the material an image field in which the focus lies and which hasan image field size, wherein the apparatus further comprises a focusadjustment device for moving a position of the focus transverse to theoptical axis and along the optical axis, a control device which isconnected to the laser device and controls the laser device such thatthe focus adjustment device moves the position of the focus of theoptical radiation in the material along a path, wherein the controldevice controls the laser device such that the cut extends parallel tothe optical axis and defines, in projection along the optical axis, acurve which has a maximum extent, wherein the focus adjustment deviceshifts the image field transverse to the optical axis to move the focustransverse to the optical axis and the control device controls the laserdevice such that, transverse to the optical axis, the cut has a maximumextent which is greater than the image field size, and defines for thefocus adjustment device a movement of the position of the focustransverse to the optical axis in the form of a movement of the positionof the focus along the curve and, defines a multi-oscillating movementof the position of the focus between an upper axial focus position and alower axial focus position during the movement along the curve.

An embodiment of the invention uses a path to produce the cut, the pathdiffering fundamentally from the usual approach which aims to minimizean axial shift of the focus as much as possible. Rather, the position ofthe focus is now adjusted much more slowly transverse to the opticalaxis (so-called lateral adjustment) than axial, by guiding the focusposition on the curve which the cut has in projection along the opticalaxis. This curve is the elevation line of the cut. It is preferably aclosed curve, e.g., a periodic Lissajous figure, for example, a circle,an ellipse etc. The focus is shifted in an oscillating mannerperpendicular thereto, i.e., axially, or along the optical axis. A pathis thus obtained which, in a side view of the cut seen perpendicular tothe optical axis, moves back and forth in a meandering shape between thelower and the upper edge of the cut corresponding to the lower and theupper axial focus position.

The cut which is produced by the method, for which the control data aredesigned and which sets the control apparatus of the machining devicedefines and sets, extends, as already mentioned, optionally onlysubstantially and not necessarily strictly, parallel to the opticalaxis. Deviations from the parallel which are small compared to thelength of the curve are acceptable. In particular in laser devices whichhave a small image field compared with the extent of the zone to betreated and which work with an image field shift, it is possible tocarry out an additional focus shift within this small image field. Thisallows, of course, to additionally deflect the position of the focuslaterally while the image field is being moved along the curve. The cutcan thereby have areas in which there is no strict parallelism to theoptical axis. Equally it is possible to produce a cut which is inclinedin relation to the optical axis at least in sections by controlling theadditional focus shift within the image field such that as a whole thecut is slightly at an angle. In this case, the additional lateral focusshift within the image field is suitably synchronized with theoscillating axial focus shift.

The movement of the focus does not necessarily require that opticalradiation be emitted onto every focus position for material to be cut.It is thus much simpler, for example, when using pulsed radiation, tocontinuously shift the focus, with the result that the spots onto whichlaser radiation pulses are emitted are spaced apart in the materialcorresponding to the path speed of the focus. If an opticalbreak-through which produces a plasma bubble is utilized for thematerial-cutting effect, it is even preferred to maintain a certaindistance between the spots onto which the individual laser radiationpulses are emitted. Methods are also known, however, in which severallaser radiation pulses cooperate to cut material without producing anoptical break-through. These approaches are also called subthresholdmethods.

Furthermore, the shift of the focus along the path described does notrule out that no laser radiation of a material-cutting effect is emittedto individual sections of the path along which the focus is guided. Inparticular, when using material cutting based on plasma bubbles,sections of the path are relevant here on which the focus is moved fromtop to bottom, i.e., in the direction of incidence of the opticalradiation. If plasma bubbles are produced for the material cutting, nofurther optical break-through and plasma bubbles can be produced inzones below a recently formed plasma bubble (which can be much biggerthan the focus) at least for some period as each plasma bubble lyingabove interferes with the focus quality in such a way that an opticalbreak-through can no longer be definitely achieved. Within the scope ofthe invention it is therefore entirely possible to blank the opticalradiation, i.e., to switch it off or at least to deactivate with respectto its material-machining effect, in those sections of the path in whichthe focus moves down, i.e., away from the laser device. Variousapproaches are known in the state of the art for such deactivations, forexample, laser-pulse lengthening, focus degradation, spectral changes,changes in polarization, etc. Within the scope of the invention, amethod is therefore advantageous in which, on sections of the path inwhich the position of the focus moves with (i.e., in the same directionas) a direction of incidence of the optical radiation, the opticalradiation is switched off or modified such that the optical radiationhas no material-cutting effect in the transparent material.

In order also in such cases to cover the cuts as closely as possiblewith sections of the path in which the optical radiation has amaterial-cutting effect, it is preferred to design the oscillation to beasymmetrical, with the result that sections of the path in which theposition of the focus moves with the direction of incidence of theoptical radiation run more steeply than sections of the path in whichthe position of the focus moves contrary to the direction of incidenceof the optical radiation.

The cut can be bi-connected in the mathematical sense. The curve is thenclosed. The cut produced can, in particular, be in the shape of acylindrical surface, which is advantageous in applications to thementioned cataract surgery. Equally, the cut can, of course, also beused to section or change transparent material, for example, eye tissue.Among other things, sectioning the crystalline lens before removal incataract surgery or the targeted weakening of the cornea with the aim ofthereby modifying the curvature of the cornea to correct defectivevision comes into consideration. In particular, but not exclusively forthese applications, closed, i.e., periodic, Lissajous figures whichcross each other are suitable. Such Lissajous figures can be achieved bycarrying out a biaxial deflection according to harmonic functions whichare based on integer multiples of a basic function, wherein the integermultiples are different for the two deflection axes.

The cut can, however, also be simply connected; the curve is then anon-closed line.

If a material cutting is carried out at the axially upper or lower focusposition, these focus positions automatically define the upper or loweredge of the cut respectively.

The shift of the image field makes it possible to dispense withexpensive optical units having an image field large enough to cover theentire treatment zone. However, it may also be pointed out that it isentirely possible to modify the treatment apparatus or the method suchthat the lateral shift of the position of the focus is done without ashift of the image field if the image field size is greater than themaximum size of the envisaged, sought or produced cut. Such an extensionlies within the scope of the invention. The advantage is then retainedthat the shift of the focus can be carried out much more slowlytransversely to the optical axis than along the optical axis. Forapplications in ophthalmology, the image field in the eye should then atleast have a diameter of approximately 5 mm.

If smaller image fields are used and it is nevertheless desired toproduce structures which have a maximum lateral extent transverselywhich is greater than the image field size, the image field can beshifted particularly easily by moving the optics or an optical elementtransverse to the optical axis. This can be done in combination with alateral focus shift within the image field.

The device and the method for producing a cut are particularlyadvantageously applicable in cataract surgery. A movable handpiece,which is placed on the eye, is required for such surgery. It istherefore preferred that the laser device has a base part and a movablehandpiece, which are connected to each other via a flexible orarticulated transmission device, wherein the focus adjustment device isformed by two parts and has a first scanner, which adjusts the positionof the focus along the optical axis and is arranged in the base part,and a second scanner, which adjusts the position of the focustransversely with respect to the optical axis and of which at least onecomponent is arranged in the handpiece. In the second scanner foradjusting the position of the focus transversely with respect to theoptical axis, this component is preferably an actuator for displacing anobjective lens transversely with respect to the optical axis.

The transmission device can preferably comprise bulk optics. It hasproved to be advantageous if the base part couples a non-collimatedlight bundle into the transmission device, thus a light bundle which hasa particular divergence or convergence state. The transmission device,for example, a corresponding articulated arm, guides this light bundlefrom the base part to the handle while maintaining divergence orconvergence state. The transverse displacement of the objective lens torealize the xy-scanning procedure is then combined with a correspondingactivation of a divergence-modifying device, which influences thedivergence or convergence of the non-collimated beam, in order tocompensate for a change in the path length which arises as a result ofthe transverse displacement of the objective lens. This prevents thetransverse displacement of the objective lens, i.e., the image fieldadjustment for the xy-scanning, from bringing with it, in an undesiredmanner, a shift of the focus position along the optical axis.

The divergence-modifying device can particularly preferably be arrangedin the base part as the handle then remains compact. It can be realizedas a telescope with an actuator that adjusts it.

The use of a non-collimated beam path between base part and handlefurther has the advantage that the z-scanner can be realizedparticularly easily by the first scanner adjusting the path length ofthe non-collimated beam path. A retroreflector, for example, a cornermirror, can be used for this path length adjustment. The use of thenon-collimated beam path makes it possible to adjust the depth positionof the focus easily by changing the path length of the beam path to theobjective lens. However, there must be a non-parallel beam path betweenthe first scanner and the objective lens since a parallel beam pathwould undo the effect of the first scanner. The beam path from thez-scanner to the objective lens is consequently not telecentric.

In an embodiment, the base part comprises a non-collimated, i.e.,diverging or converging beam path section and the first scannercomprises a corner mirror, which lies in this beam path section. Toshift the position of the focus along the optical axis, the cornermirror is displaced in order to change the length of the non-collimatedbeam path section.

The corner mirror can be displaced particularly quickly by anoscillator, which makes the corner mirror vibrate to periodically changethe length of the non-collimated beam path section. Alternatively, it ispossible to mount several corner mirrors on a rotating disc, which passthrough the non-collimated beam path section one after the other.

It is understood that the features mentioned above and those yet to beexplained below can be used, not only in the stated combinations, butalso in other combinations or singly, without departing from the scopeof the present invention. The description of method features formaterial cutting or for producing control data also relates equally to acorresponding embodiment of the control device, which controls thetreatment apparatus. Conversely, features which are described inrelation to the treatment apparatus, in particular its control device,are equally relevant to the corresponding method for material treatmentor for producing control data.

The production of control data can be carried out separately from, i.e.,independently of, the treatment apparatus. Of course, it presupposescorresponding knowledge about the treatment apparatus for which thecontrol data are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail below by way of examplewith reference to the attached drawings which also disclose features ofthe invention wherein:

FIG. 1 depicts a schematic representation of an embodiment of atreatment apparatus for ophthalmological surgery, in particular forcorrecting defective vision,

FIG. 2 depicts a schematic representation with regard to the structureof the treatment apparatus of FIG. 1,

FIG. 3 depicts a basic principle for introducing pulsed laser radiationinto the eye with the treatment apparatus of FIG. 1,

FIG. 4 depicts a schematic representation of a cut through a capsularbag of an eye,

FIG. 5 depicts a schematic representation of the cut represented in FIG.4,

FIG. 6 depicts a schematic representation similar to FIG. 5 toillustrate the guiding of the laser beam on a path,

FIG. 7 depicts a schematic representation of a cut which, unlike the cutin FIG. 4, does not surround a zone,

FIG. 8 depicts a schematic representation similar to FIG. 4 illustratinga possible application of the cut of FIG. 7,

FIG. 9 depicts a schematic representation of a treatment apparatus thatis designed for cataract surgery,

FIG. 10 depicts a schematic representation of a handle of the treatmentapparatus of FIG. 9,

FIG. 11 depicts a schematic representation of a z-scanner of thetreatment apparatus of FIG. 9,

FIG. 12 depicts a schematic block diagram for the control concept of thetreatment apparatus of FIG. 9, and

FIGS. 13 and 14 depict schematic representations for alternativeembodiments of the z-scanner of the treatment apparatus of FIG. 9.

DETAILED DESCRIPTION

FIG. 1 shows a treatment apparatus 1 for eye surgery. For example, aneye-surgery process which is similar to that described in EP 1 159 986A2 and U.S. Pat. No. 5,549,632 can be carried out with it. The treatmentapparatus 1 produces a material cutting in transparent material by meansof treatment laser radiation 2. This material cutting can be e.g., aproduction of cuts, in particular the treatment apparatus for correctingdefective vision can generate a change on an eye 3 of a patient 4. Thedefective vision can include hyperopia, myopia, presbyopia, astigmatism,mixed astigmatism (astigmatism in which there is hyperopia in onedirection and myopia in a direction at right angles thereto), asphericerrors and higher-order aberrations. The material cutting can be used inthe field of corneal surgery but also on other tissues of the eye, e.g.,in cataract surgery. While reference is made to eye surgery below, thisis to be understood in each case only by way of example and not aslimiting.

In the embodiments described, the components of the apparatus 1 arecontrolled by an integrated control unit, which, however, can of coursealso be provided as a stand-alone unit.

FIG. 2 shows the treatment apparatus 1 schematically. In this variant ithas at least three devices or modules. Laser device L emits the laserbeam 2 onto the material, e.g., an eye, via optics O and moves theposition of the focus in the material in three spatial directions. Theshift along the main direction of incidence of the optical radiation(z-axis) is called axial shift and the shift perpendicular thereto iscalled lateral shift. In the variant shown in FIG. 2, the optics O hasan image field B, in which a focus 6 of the laser radiation 2 lies,which image field is smaller than the extent of the zone to be treated.In order to shift the position of the focus 6 in the material lateral,the objective lens of the laser device L is displaced transverse to theoptical axis. This is indicated in FIG. 2 by a double arrow for theobjective lens. The focus 6 together with the image field B is therebydisplaced. Optionally, the focus 6 can additionally be fine shifted inan area S within the image field B.

In an alternative variant, the laser device L has lateral scanningdevice, which shifts the focus 6 in the image field B, which is largeenough to cover the extent of the zone to be treated. An axial scanningdevice is additionally provided.

In all variants, the operation of the laser device L is fully automatic,controlled by integrated or separate control device C. In response to acorresponding start signal the laser device L starts to move the laserbeam 2 and thereby produces cuts in a manner yet to be described.

The control device C operates according to control data which eitherhave been produced by it or have been supplied to it. In the lattercase, which is shown in FIG. 2, the control data necessary for operationare supplied to the control device C beforehand as a control data set byplanning device P via control lines not identified in more detail. Thedetermination or transmission of the control data takes place prior tooperation of the laser device L. Of course, the communication can alsobe wireless. As an alternative to direct communication, it is alsopossible to arrange the planning unit P physically separated from thelaser unit L, and to provide a corresponding data transmission channel.

In ophthalmology, the defective vision of the eye 3 is preferablymeasured with one or more measuring devices M before the treatmentapparatus 1 is used. The measured values are then supplied to thecontrol device or the planning device P and form the basis for theproduction of control data. In particular, the position and/or extent ofan area to be treated, in particular to be sectioned, can be measured.

The control device or the planning device P produces the control dataset from the measurement data which have been determined, e.g., for theeye to be treated. They are supplied to the planning device P via aninterface S and, in the embodiment shown, come from measuring device Mwhich has previously taken measurements of the eye of the patient 4. Ofcourse, the measuring device M can transfer the correspondingmeasurement data to the planning device P or directly to the controldevice C in any desired manner.

In the embodiment described, the laser radiation 2 is focussed as apulsed laser beam into the material, e.g., the eye 3. The pulse durationproduced by the laser device L in this case is e.g., in the femtosecondrange, and the laser radiation 2 acts through non-linear optical effectsin the material, e.g., the capsular bag, the crystalline lens or thecornea. The laser beam has laser pulses as short as e.g., 50 to 800 fs(preferably 100-400 fs) with a pulse repetition frequency of between 10kHz and 10 MHz. The type of material-cutting effect which the treatmentapparatus 1 utilizes with the laser radiation 2, however, is of nofurther relevance for the following description, in particular there isno necessity to use pulsed laser radiation, though a focus of treatmentradiation 2 in the material should be shifted along a path.Alternatively, UV radiation (300 to 400 nm), in particular with awavelength of approximately 355 nm and a pulse duration of between 0.1and 10 ns, can be used.

The treatment apparatus 1 generates a cut in the material, the shape ofwhich cut depends on the pattern with which the laser-pulse fociare/become arranged in the tissue. The pattern in turn depends on thepath along which the focus is shifted. The path predetermines targetpoints for the focus position to which one or more laser pulse(s) is(are) emitted and ultimately defines the shape and position of the cut.

A possible effect of the laser beam 2 is indicated schematically in FIG.3. It is focussed into the material, e.g., the cornea 5 or lens of theeye by means of optics of the laser device L, not identified in moredetail. As a result, a focus 6 forms in the material in which focus theenergy density of the laser radiation is so high that, in combinationwith the pulse length, a non-linear effect occurs. For example, eachpulse of the pulsed laser radiation 2 can produce at the respective spotof the focus 6 an optical break-through in the material, e.g., in thecornea 5 or lens, which is indicated schematically in FIG. 3 by way ofexample by a plasma bubble. As a result, material, e.g., tissue, is cutby this laser pulse. When a plasma bubble forms, the tissue layer isdisrupted in a zone larger than the spot covered by the focus 6 of thelaser radiation 2, although the conditions for producing thebreak-through are achieved only in the focus. In order for an opticalbreak-through to be produced by every laser pulse, the energy density,i.e., the fluence, of the laser radiation must be above a certainthreshold value which is dependent on wavelength and pulse length. Thisrelationship is known to a person skilled in the art, for example, fromDE 695 00 997 T2.

Alternatively, a material-cutting effect can also be produced throughthe pulsed laser radiation by emitting several laser radiation pulses inthe one area, wherein the spots 6, i.e., sites of the focus 6, overlapfor several laser radiation pulses. Several laser radiation pulses theninteract to achieve a tissue-cutting effect, without plasma bubblesforming (so-called subthreshold regime). For example, the treatmentapparatus 1 can use the principle which is described in WO 2004/032810A2.

By way of example, FIG. 4 shows the production of a cut 9 in a capsularbag which envelops a lens 8 of the eye 3. The cut 9 is bi-connected. Ithas the shape of a circular cylinder jacket, thus the lateral area of acylinder, the generatrix of which is a circular curve K; however, otherclosed figures are also possible as generatrix of the cylinder, inparticular any periodic Lissajous figure, including a crossing one.

The curve K defines the lateral shift of the focus, i.e., in thex/y-plane. The corresponding x/y-coordinates lie in the plane of theimage field B of the laser device L. They are plotted in the figures byway of example. The position of the focus 6 is moved along the curve Kperpendicular to the optical axis OA, which is the main direction ofincidence of the optical laser radiation 2. Simultaneously the axialposition of the focus oscillates along the optical axis OA, i.e.,perpendicular to the x/y-plane. A path 10, which oscillates back andforth between an upper axial focus position z1 and a lower axial focusposition z2, thereby generates the cut 9. These oscillations are carriedout several times during the movement along the curve K.

This procedure avoids rapid lateral deflection of the laser radiation 2over the zone to be treated, which is characterized in the describedcase by the radius R of the curve K and has a maximum lateral dimensionof 2*K. Optionally, a size of the image field B is much smaller thanthis lateral extent. Generally, a rapid axial movement is carried out,while the lateral movement follows the curve K in the x/y-plane. A cutis thus produced which is substantially parallel to the optical axis. Asimple optical system can thus be used which does not require a rapidbut long-stroke lateral shift of the focus.

Several approaches come into consideration for the axial focus shift,for example, an electro-optical lens or a so-called two-stage z-scanner,which combines a slow, long-stroke shift with a rapid, short-strokeshift. The two stages of such a two-stage z-scanner can be formedspatially separated or combined.

For the case of treatment of the human lens, which is to be dealt withby way of example in the following, a maximum value NA=0.2 cannot besubstantially exceeded for anatomical reasons. From this the effectivefocal length of the objective lens used results at least approximatelyat:

$f \approx \frac{n \cdot D}{2 \cdot {NA}} \approx \frac{{1.3 \cdot 6}\mspace{14mu} {mm}}{2 \cdot 0.2} \approx {19\mspace{14mu} {{mm}.}}$

In order to travel the path 10, the axial shift must follow a pathaccording to:

ζ(t)=ζ_(max) sin(ω·t).

For the acceleration the following is obtained corresponding by:

{umlaut over (ζ)}(t)=−ω ²·ζ_(max) sin(ω·t)

The typical radius R for the curve K is between 2 and 3 mm in cataractsurgery. The circumference of the cut is therefore approximately 20 mm.In order to achieve good material cutting in a technique based on plasmabubbles, the tangential path dimension (adjacent axial oscillations)should be between 1 and 10 μm. Approximately between 2,000 and 20,000vertical cut path sections are thus to be produced. The spacing betweenthe spots should be in the order of between 1 and 10 μm on each cut pathsection.

The height H must correspond at least to the thickness of the capsularbag, thus approximately to 20 to 25 μm. If it is smaller, several cuts 9can be “stacked” on top of each other in order to sever the capsularbag, wherein a certain overlap can be useful.

A total height of from 25 μm to 250 μm seems to be practical. The cut 9thus has a unit area of from approximately 500,000 to 5,000,000 μm².50,000 to 5,000,000 laser spots are thus positioned with a grid constantof from 1×1 μm to a maximum of 10×10 μm.

At a laser pulse repetition rate of 100 kHz, a minimum cut productiontime (without breaks or down times) of from 0.5 to 50 s results. Sincepulse energies in the μJ range can be easily produced at such a laserpulse repetition rate it is preferred to combine a larger average spotdistance with higher energy, e.g., 0.5 μJ and 3×3 μm. The productiontime for the cut is thus only a few seconds (less than 10 s) even in thecase of tall cylinders.

Alternatively, with low pulse energy (<100 nJ) and a laser pulserepetition rate in the range of a few MHz a spot distance of 1×1 μm canbe used. For example, at 5 MHz a production time for the cut of only afew seconds (less than 10 s) likewise is obtained again.

This means that the axial adjustment must realize 2,000 to 20,000 axialoscillations within approximately 5 seconds during the lateral circuitaround the curve K having a circumference of 20 mm depending on the pathdistance. The axial frequency (oscillation frequency) is thus 500 Hz to5 kHz. For the acceleration the following results:

Max({umlaut over (ζ)}(t))=ω ²·ζ_(max)=4π² f ²·ζ_(max)≈10^(6 . . . 11) s⁻²·ζ_(max).

It is to be borne in mind that the type of the path 10 does notautomatically prevent unfavorable influencing of the optical beam paththrough the material (tissue) by previous interactions, as would be thecase in the layer-by-layer construction of the cut along the directionof incidence of the laser radiation. Therefore, according to FIG. 6, arefinement is provided, by modifying the laser radiation 2 on sections11 of the path 10 into the depth of the material (away from thedirection of incidence) such that no interaction occurs which mightinterfere with the transmission of subsequent pulses, or this is atleast reduced. In the simplest case, the pulses are completelysuppressed on these sections 11. This concept can also be extended tothe areas near the reversal points of the path, thus up to approximately40% in the vicinity of the turning points of the path 10 (notnecessarily symmetrically).

FIG. 7 shows by way of example a cut 9, which is simply connected in themathematical sense, the curve K of which is thus not closed to form aloop. The maximum dimension of the cut 9 thus results from the length 13of the curve K. The focus is, in turn, shifted lateral along the curveK. While travelling the length 13 the focus is at the same time shiftedaxial in an oscillating manner.

The absolute position of the axial upper and lower focus position variesalong the curve K. This is, of course, not compulsory; constant axialupper and lower focus positions can also be used, too. There is just aslittle need for the distance between the axial upper and lower focusposition, between which the oscillation is carried out, to be constant.As a result, the position of the focus follows the meandering path 10 inthe cut 9, and the axial upper and lower focus position(s) of theoscillation predetermine(s) the upper and lower edge of the cut 9respectively. This is equally possible for bi-connected cuts.

FIG. 8 shows by way of example possible applications for such cuts. Ineach case two cuts are represented in turn on a capsular bag, envelopinga crystalline lens. Two cuts 9.1 and 9.2 which have curves K.1 and K.2are shown by way of example.

The left-hand cut 9.1 is an example wherein the upper and lower focusposition can vary during the movement along the curve K.1. Theoscillation along the trajectory 10.1 is thus synchronized with theposition along the curve K.1, with the result that e.g., the cut isproduced in the shape of a circular disc shown in FIG. 8. It is thuspossible, as shown in the embodiment of FIG. 8, to restrict the cut to adesired section of the transparent material, to the crystalline lenshere, without impairing other material structures, the capsular baghere.

The right-hand cut 9.2 illustrates that the cut can also deviate frombeing strictly parallel to the optical axis OA. As in the left-hand cut9.1, the axial focus shift here is also synchronized with the lateralfocus shift. Now, however, the effect is that an additional lateralfocus shift synchronized to the axial focus shift is carried out inorder to incline the cut 9.2 slightly against the optical axis OA. Ofcourse, this inclination can also be restricted to sections of the cut9.2. This additional lateral focus shift is to be achieved particularlysimply in the treatment apparatus of FIG. 2 when the focus is shiftedadditionally in a suitable manner within the image field B. The cut 9.2is still substantially parallel to the optical axis OA, since theadditional lateral focus shift in synchronization with the axial focusshift is small compared with the extent of the curve K.

The axial focus shift can be carried out simply if the amplitude can beminimized. This is preferably the case when a z-scanner is configuredsuch that the optical scale ratio of focus movement to z-scannermovement is less than 1:2, preferably even less than 1:1. This meansthat the mechanical path variation in the scanner is not greater thanthe focus movement in the object. The acceleration is then in the rangeof from 0.1 to 10³ m/s².

An optional means for achieving such a value is a reflective z-scanner,the optical design of which is provided to avoid a beam focus in aconventional scan path being positioned on an optical boundary surfaceof the scanner.

A further optional means consists of the z-scanner having, as a drive, apiezo stack or a plunger coil which is operated as resonantly aspossible. It is also an option to bring about the reflection by means ofan electro-optical component (e.g., AOM).

As mentioned, a second z-scanner can also be used, which realizesadditional divergence changes (positive or negative) of the laser beamthat are slow over time, wherein the scanner is controlled by a controlunit, which takes into account the position signals (measurement signal)or control signals of one scanner during the control of the respectivelyother scanner, because, for example, both control signals are producedin the control unit. The control unit can be realized by the controldevice 6.

The treatment apparatus 1 represented schematically in FIG. 9 provides arapid variation of the focus position along the optical axis, i.e., arapid z-scanner, for the field of ophthalmological surgery, inparticular for cataract surgery. In this treatment apparatus 1, elementswhich have already been explained with reference to the previous figuresand which have the same function or structure in the treatment apparatus1 are provided with the same reference numbers and are therefore notnecessarily explained again.

The treatment apparatus 1 has a base part 15, which provides the laserradiation 2 and a handpiece 16, to which the laser radiation istransmitted. The transmission takes place by means of an articulated arm17, which preferably has free space optics, which can be realized, forexample, by suitable deflecting mirrors (not shown). It isdisadvantageous to use optical fibers, as there are problems related tothe radiation intensities of the laser radiation 2 required. However,optical fibers can be used in or instead of the articulated arm 17.

The handle 16 is placed on the eye 3. It is shown in detail in FIG. 10and explained below.

The z-scanner and xy-scanner are realized in the base part 15 and in thehandpiece 16. Both elements thus form, together with the articulated arm17, the laser device L. The z-scanner is provided in the base part 15 inthe structure of FIG. 9. A laser source 18 emits the laser radiation 2,which is transmitted via a deflecting mirror 19 and a lens 20 into anon-collimated beam path in the z-scanner 21, the structure of whichwill be explained below with reference to FIGS. 11, 13 and 14. Thez-scanner outputs, the laser radiation 2 to the articulated arm 17 via adeflecting mirror 22 and lenses 23, 24 as a non-collimated beam. Thelenses 23, 24 form a telescope, which can be adjusted via a drive 25.The significance of this telescope will be explained below.

When configured as bulk optics, the articulated arm 17 contains a seriesof deflecting mirrors and optionally a relay optical unit, in order totransmit the non-collimated beam to the output side of the articulatedarm.

The handpiece 16 receives the laser radiation 2 as a non-collimated beamfrom the articulated arm 17 and outputs it into the eye 3 via a contactlens 27. A grip 26 is provided for positioning the handpiece 16.

The laser radiation 2 is guided in the handpiece 16 via deflectingmirrors 28 and 29 to an objective lens 30, which is displaced by anactuator 31 transverse to the optical axis. This realizes thealready-mentioned image field shift. The objective lens 30 is not afield objective lens, i.e., not an objective lens which is telecentricon the image side, but, the laser radiation is focussed into differentdepths in the eye 3 depending on the divergence or convergence of thebeam at the entrance pupil of the objective lens 30. Thus the variationin the propagation of the beam brought about by the z-scanner isconverted into a variation in the axial focus position in the eye 3.

To adjust the image field, the objective lens 3 is moved laterally inthe handpiece 16 by the actuator 31. At the same time, the deflectingmirrors 28 and 29 in the handpiece 16 are mechanically controlled andrepositioned by the control device C for the displacement of theobjective lens 30 such that the laser radiation 2 always remains acentered beam in the entrance pupil of the objective lens.

FIG. 11 shows the effect of the z-scanner 21 schematically. It has acorner mirror 31, which realizes a retroreflector. In principle, thecorner mirror 31 can be replaced by any different type ofretroreflector. The corner mirror 31 is fixed to a tuning fork 32, whichis made to vibrate by an exciter 33. The corner mirror is illuminated bythe non-collimated beam of the laser radiation 2. By adjusting theposition of the corner mirror, the length of the non-collimated beampath is changed, and thus the propagation of the diverging beam of thelaser radiation 2.

FIGS. 13 and 14 show alternatives for the scanner 21. According to FIG.13, a large number of corner mirrors 31 are fixed on a rotating disc 34,which is made to rotate about an axis 35. The rotation has the effectthat the optical path length of the diverging beam section is adjusted.The advantage is a more rapid adjustment, the disadvantage is a lowerrepeat accuracy and an increased outlay on adjustment for the severalcorner mirrors 31. FIG. 14 shows another refinement, which in additionto the structure of FIG. 13 also has an end mirror 36 and a beamsplitter 35. The incident, diverging beam of the laser radiation 2passes through the beam splitter 37, is deflected at the corner mirror31 to the end mirror 36, reflected there (from now on the beam path isshown by a dashed line), reflected again by the corner mirror 31 andthen coupled out by the beam splitter 37. The path length adjustmentwhich occurs during the rotation of the disc 34 is thus twice as large,with the result that a higher adjustment speed is achieved at the samerotation speed of the disc 34.

In order to generate targeted cuts in the eye according to theabove-described cut methodology, the actuator 31 move the objective lens31 laterally in the handpiece 16 (by repositioning the deflectingmirrors 28 and 29). During this lateral movement, the telescope 23, 24is readjusted synchronously by the drive 25. This is necessary becausethe optical path length from the scanner 21 to the objective lens 30varies due to the lateral movement of the objective lens 31. Since thebeam of the laser radiation 2 is non-collimated when it strikes theobjective lens 30, the change in path length would additionally lead toa change in the z position of the focus. The desired z-scanner propertywould thus be disrupted. The divergence/convergence of the light beam istherefore adjusted synchronously with the movement of the objective lens30 with the aid of the telescope 23, 24.

FIG. 12 shows a block diagram of a control set-up provided for thispurpose. Here the control device C is shown in the form of threefunctions. A central control block CC controls two sub-blocks, a controlblock CT to control the telescope 23, 24 and a control block CO for theactuator 31, i.e., to displace the objective lens 30. The synchronizedcontrol of the shift of the transverse position of the objective lens 30and of the shift of the telescope 23, 24 has the result that theposition of the focus in the depth direction is exclusively set by thez-scanner 21, and that the shift of the image field B does not bringwith it a simultaneous displacement of the depth position of the focus.In other words, the synchronous shift of the telescope 23, 24 being ameans of influencing the divergence/convergence of the radiationstriking the objective lens 30 and the transverse shift of the objectivelens ensure that the image field is moved in a plane perpendicular tothe optical axis and not on a curved trajectory.

When treating cataracts it is advantageous to provide navigationproperties which make it possible to determine the position of thestructures to be treated, for example, the position of the capsular bagor the lens. In a system with a mechanically-movable optical unit forthe lateral focus shift, which has an image field which is smaller thanthe structure to be found or the cut to be produced, different variantscome into consideration.

Variant 1—Confocal detection: For measuring the topography of the eye 3in the area of the cornea 5 and/or the lens 8, back-reflected light isdeflected with the aid of polarization optical units, focussed on adiaphragm and recorded using a photodetector. The wavelength of thelaser radiation 2 is used for this measurement. Using the z-scannerconfocal signals from a small scanning range of 10-100 μm are sensed.The signals recorded by the photodetector are amplified e.g., with alock-in method or boxcar integrator. The reference frequency for thelock-in amplifier equals the scanning frequency of the rapid z-scanner.The confocal signals are recorded during the (slow) movement of theobjective lens. The image field B moves along the curve K, which matchesthe pattern for the laser treatment. At the same time, the axial focusposition is adjusted, with the result that a path (e.g., the path 10) istraveled. In this way, the exact position is determined where laserdesorption is to take place and thus the safety of the treatment isincreased.

Variant 2—OCT detection: In this variant, the topography of the eye 3 inthe area of the cornea 5 and/or the lens 8 is measured usingshort-coherent light, which has a different wavelength. The light from ashort-coherent source is coupled into the optical unit O using adichroic mirror. The light reflected back by eye structures is deflectedby the same dichroic mirror and detected using an interferometricarrangement. In order to make the laser treatment safe and precise, anobjective lens is used which has a numerical aperture in the range0.15-0.2. In a fully-illuminated entrance pupil of the objective lens,the z-axial measurement range of the OCT detection is limited by thedepth of field of the objective lens. Accordingly, here theshort-coherent illumination is designed (e.g., by correspondingselection of the collimator geometry or using a diaphragm) such thatonly part of the entrance pupil of the objective lens O is illuminated.Since the effective numerical aperture of the focussed short-coherentlight is thereby reduced, a larger depth range is realized here for theOCT detection.

Preferably, in these navigation measurements, no tomographic imageacquisition of the eye structures occurs, but is simulated and matchedto a computational eye model using depth-resolved measurements atselected points the eye structure. The result of this matching isrepresented as an optional animation. Using this animation, the surgeonis in a position to set the spatial boundaries of the photodesorption.

In an embodiment, the depth-resolved navigation measurements take placealong the path which is used for the laser treatment. If thesemeasurements reveal a decentering of the circular pattern of the plannedcapsular bag opening in relation to the crystalline lens, optionally, anew series of navigation measurements is taken. The data obtained inthis way are correlated again with the computational eye model and theresult is displayed as an animation for checking the laser treatment.

1. A treatment apparatus for producing a cut in a transparent material,the apparatus comprising: a laser device which is adapted to generate acut within the transparent material using optical radiation, the laserdevice a control device which is connected to the laser device andcontrols the laser device such that a focus adjustment device moves theposition of the focus of the optical radiation in the material along apath, wherein the control device controls the laser device such that thecut has, in projection along an optical axis, a form of a curve,
 2. Amethod for producing control data for producing a cut in a transparentmaterial, wherein the control data are designed for a laser devicecomprising: optics configured to focus the optical radiation along anoptical axis into a focus situated in the material and which have in thematerial an image field in which the focus lies and which has an imagefield size, and a focus adjustment device for moving a position of thefocus, wherein the control data are produced to comprise data for thefocus adjustment device defining a movement of the position of the focusalong a curve.
 3. A method for producing a cut in a transparentmaterial, in particular eye tissue, the method comprising focussingoptical radiation into the transparent material, generating a cut byshifting a focus within the material along a path which is located inthe cut, wherein a position of the focus is moved transverse to theoptical axis along the curve.